diff --git a/prism/prism.c b/prism/prism.c
index 05123ac570..09f25fa8a9 100644
--- a/prism/prism.c
+++ b/prism/prism.c
@@ -18508,7 +18508,12 @@ parse_expression_prefix(pm_parser_t *parser, pm_binding_power_t binding_power, b
                     lex_state_set(parser, PM_LEX_STATE_BEG);
                     parser->command_start = true;
 
-                    expect1(parser, PM_TOKEN_PARENTHESIS_RIGHT, PM_ERR_DEF_PARAMS_TERM_PAREN);
+                    if (!accept1(parser, PM_TOKEN_PARENTHESIS_RIGHT)) {
+                        PM_PARSER_ERR_TOKEN_FORMAT(parser, parser->current, PM_ERR_DEF_PARAMS_TERM_PAREN, pm_token_type_human(parser->current.type));
+                        parser->previous.start = parser->previous.end;
+                        parser->previous.type = PM_TOKEN_MISSING;
+                    }
+
                     rparen = parser->previous;
                     break;
                 }
diff --git a/prism/templates/src/diagnostic.c.erb b/prism/templates/src/diagnostic.c.erb
index cffaf0853d..75a00958fc 100644
--- a/prism/templates/src/diagnostic.c.erb
+++ b/prism/templates/src/diagnostic.c.erb
@@ -149,7 +149,7 @@ static const pm_diagnostic_data_t diagnostic_messages[PM_DIAGNOSTIC_ID_MAX] = {
     [PM_ERR_DEF_ENDLESS_SETTER]                 = { "invalid method name; a setter method cannot be defined in an endless method definition", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_DEF_NAME]                           = { "unexpected %s; expected a method name", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_DEF_PARAMS_TERM]                    = { "expected a delimiter to close the parameters", PM_ERROR_LEVEL_SYNTAX },
-    [PM_ERR_DEF_PARAMS_TERM_PAREN]              = { "expected a `)` to close the parameters", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_DEF_PARAMS_TERM_PAREN]              = { "unexpected %s; expected a `)` to close the parameters", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_DEF_RECEIVER]                       = { "expected a receiver for the method definition", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_DEF_RECEIVER_TERM]                  = { "expected a `.` or `::` after the receiver in a method definition", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_DEF_TERM]                           = { "expected an `end` to close the `def` statement", PM_ERROR_LEVEL_SYNTAX },